Method for measuring frequency stability of a cryogenic monocrystalline silicon optical cavity

Abstract

The application provides a method for measuring the frequency stability of a low-temperature single-crystal silicon optical cavity, and relates to the technical field of lasers.The method comprises the following steps: providing a single-crystal silicon optical cavity to be measured; using a refrigerator to reduce the temperature of the single-crystal silicon optical cavity, and reducing the temperature of the single-crystal silicon optical cavity to a first preset temperature; after the temperature of the single-crystal silicon optical cavity is reduced to the first preset temperature, the refrigerator is turned off; during the period when the refrigerator is turned off, and when the vibration amplitude of the refrigerator is reduced to a first preset value, the frequency of the single-crystal silicon optical cavity is obtained; and based on the frequency of the single-crystal silicon optical cavity, the frequency stability of the single-crystal silicon optical cavity is obtained. Since the refrigerator is turned off and the vibration amplitude of the refrigerator is reduced to the first preset value, the influence of the vibration of the refrigerator on the frequency stability of the single-crystal silicon optical cavity can be eliminated, and the influence of the vibration amplitude of the refrigerator on the accurate measurement of the frequency stability of the single-crystal silicon optical cavity can be effectively inhibited.

Description

Technical Field

[0001] This application relates to the field of laser technology, and in particular to a method for measuring the frequency stability of a low-temperature single-crystal silicon optical cavity. Background Technology

[0002] Low-temperature single-crystal silicon optical cavities are optical cavities made of single-crystal silicon, with a temperature of approximately 3-5 Kelvin (around -270°C). These cavities require cooling to maintain this temperature at approximately 3-5 Kelvin (around -270°C). However, vibrations inevitably occur during the cooling process, leading to vibration noise during the measurement of the frequency stability of the single-crystal silicon optical cavity. Therefore, how to suppress the vibration noise of the cooling system on the accurate measurement of the inherent high frequency stability of the single-crystal silicon optical cavity has become a key issue for those skilled in the art. Summary of the Invention

[0003] In view of this, this application provides a method for measuring the frequency stability of a low-temperature single-crystal silicon optical cavity, as follows:

[0004] A method for measuring the frequency stability of a low-temperature single-crystal silicon optical cavity, comprising:

[0005] Provide a single-crystal silicon optical cavity to be tested;

[0006] The temperature of the single-crystal silicon optical cavity is reduced to a first preset temperature by using a refrigerator.

[0007] After the temperature of the single-crystal silicon optical cavity drops to the first preset temperature, the refrigerator is turned off. During the period when the refrigerator is turned off, and when the vibration amplitude of the refrigerator drops to the first preset value, the frequency of the single-crystal silicon optical cavity is obtained.

[0008] The frequency stability of the single-crystal silicon optical cavity is obtained based on its frequency.

[0009] Optionally, after the temperature of the single-crystal silicon optical cavity drops to the first preset temperature, the refrigerator is turned off, and during the period when the refrigerator is turned off, and when the vibration amplitude of the refrigerator drops to the first preset value, the frequency of the single-crystal silicon optical cavity is obtained including:

[0010] After the temperature of the single-crystal silicon optical cavity drops to the first preset temperature, the refrigerator is turned off.

[0011] During the period when the refrigerator is off, when the refrigerator changes from a first state to a second state, and during the maintenance of the second state, the frequency of the single-crystal silicon optical cavity is acquired;

[0012] When the refrigeration unit is in the second state, the vibration amplitude of the refrigeration unit is reduced to the first preset value, and the vibration amplitude of the refrigeration unit in the first state is greater than the vibration amplitude in the second state.

[0013] Optionally, during the maintenance of the second state, obtaining the frequency of the single-crystal silicon optical cavity includes:

[0014] During the first preset time period of the second state maintenance process, the frequency of the single-crystal silicon optical cavity is obtained;

[0015] There is a second preset time between the first preset time and the start time of the second state. The value of the second preset time is greater than 0, and the value of the first preset time is in the range of 40s to 60s, including the endpoint value.

[0016] Optionally, after the temperature of the single-crystal silicon optical cavity drops to the first preset temperature, the refrigerator is turned off, and during the period when the refrigerator is turned off, and when the vibration amplitude of the refrigerator drops to the first preset value, obtaining the frequency of the single-crystal silicon optical cavity further includes:

[0017] During the maintenance of the second state, the temperature of the single-crystal silicon optical cavity is acquired;

[0018] If the temperature of the single-crystal silicon optical cavity is higher than the second preset temperature, the acquisition of the frequency of the single-crystal silicon optical cavity is stopped, and the refrigerator is started to cool down the single-crystal silicon optical cavity to the first preset temperature.

[0019] After the temperature of the single-crystal silicon optical cavity is reduced back to the first preset temperature, the refrigerator is turned off, and during the period when the refrigerator is turned off, and when the vibration amplitude of the refrigerator is reduced to the first preset value, the frequency of the single-crystal silicon optical cavity is obtained.

[0020] Optionally, cooling the single-crystal silicon optical cavity using a refrigerator to reduce the temperature of the single-crystal silicon optical cavity to a first preset temperature includes:

[0021] The single-crystal silicon optical cavity is placed in the sample chamber of the refrigerator;

[0022] The sample chamber of the refrigerator is evacuated for the first time using the first vacuum pumping device to bring the sample chamber of the refrigerator to a first vacuum level.

[0023] The sample chamber of the refrigerator is evacuated a second time using a second vacuum device to bring it to a second vacuum level; wherein the second vacuum level represents a higher degree of vacuum than the first vacuum level.

[0024] After the sample chamber of the refrigerator is evacuated to the second vacuum level, the refrigerator is used to cool the single-crystal silicon optical cavity, reducing the temperature of the single-crystal silicon optical cavity to the first preset temperature.

[0025] Optionally, a single-crystal silicon optical cavity is provided, comprising:

[0026] The single-crystal silicon optical cavity is provided with a cavity length of a first cavity length;

[0027] Provide a first reference cavity with a cavity length of the second cavity length;

[0028] Provide a second reference cavity with a cavity length of the third cavity length;

[0029] The temperature difference between the first reference cavity and the second reference cavity is not greater than a second preset value, and the temperature range of the first reference cavity and the second reference cavity is 15℃~30℃, including the endpoint values.

[0030] Optionally, after the temperature of the single-crystal silicon optical cavity drops to the first preset temperature, the refrigerator is turned off, and during the period when the refrigerator is turned off, and when the vibration amplitude of the refrigerator drops to the first preset value, the frequency of the single-crystal silicon optical cavity is obtained including:

[0031] After the temperature of the single-crystal silicon optical cavity drops to the first preset temperature, the refrigerator is turned off. During the period when the refrigerator is turned off, and when the vibration amplitude of the refrigerator drops to the first preset value, the frequency of the single-crystal silicon optical cavity is obtained.

[0032] Furthermore, while acquiring the frequency of the single-crystal silicon optical cavity, the frequencies of the first reference cavity and the second reference cavity are also acquired.

[0033] Optionally, obtaining the frequency stability of the single-crystal silicon optical cavity based on its frequency includes:

[0034] The frequency stability of the single-crystal silicon optical cavity is obtained based on the frequency differences between any two of the single-crystal silicon optical cavity, the first reference cavity, and the second reference cavity.

[0035] The frequency stability of the single-crystal silicon optical cavity is obtained based on the frequency differences between any two of the three cavities: the single-crystal silicon optical cavity, the first reference cavity, and the second reference cavity.

[0036] The frequency stability of the single-crystal silicon optical cavity is obtained based on the first frequency difference, the second frequency difference, and the third frequency difference.

[0037] The first frequency difference is the frequency difference between the frequency of the single-crystal silicon optical cavity and the frequency of the first reference cavity, the second frequency difference is the frequency difference between the frequency of the single-crystal silicon optical cavity and the frequency of the second reference cavity, and the third frequency difference is the frequency difference between the frequency of the first reference cavity and the frequency of the second reference cavity.

[0038] Optionally, the first reference cavity is made of ULE glass, and the second reference cavity is made of ULE glass.

[0039] Optionally, the lengths of the first cavity, the second cavity, and the third cavity are equal; or

[0040] The lengths of the first cavity, the second cavity, and the third cavity are not equal; or

[0041] The lengths of the first cavity and the second cavity are not equal, while the lengths of the second cavity and the third cavity are equal.

[0042] Compared with related technologies, the beneficial effects of the technical solution in this application are as follows:

[0043] The measurement method includes: providing a single-crystal silicon optical cavity to be measured; cooling the single-crystal silicon optical cavity using a refrigerator to reduce its temperature to a first preset temperature; after the temperature of the single-crystal silicon optical cavity is reduced to the first preset temperature, turning off the refrigerator, and acquiring the frequency of the single-crystal silicon optical cavity while the refrigerator is off and the vibration amplitude of the refrigerator is reduced to a first preset value; and acquiring the frequency stability of the single-crystal silicon optical cavity based on its frequency. Since the refrigerator will not vibrate due to its operation after being turned off, it will not shake the experimental platform containing the single-crystal silicon optical cavity, thus preventing the vibration of the refrigerator from affecting the cavity length of the single-crystal silicon optical cavity, and consequently preventing the vibration of the refrigerator from affecting the measurement of the inherent frequency stability of the single-crystal silicon optical cavity. Therefore, when the refrigerator is turned off and the vibration amplitude of the refrigerator is reduced to the first preset value, the frequency stability of the obtained single-crystal silicon optical cavity will not be affected by the vibration of the refrigerator. That is, the influence of the vibration amplitude of the refrigerator on the frequency stability of the single-crystal silicon optical cavity can be effectively avoided, thereby obtaining the frequency stability of the single-crystal silicon optical cavity when it is in a low-temperature state.

[0044] Furthermore, this measurement method acquires the frequency of the single-crystal silicon optical cavity when the refrigerator is off, thereby measuring the frequency stability of the single-crystal silicon optical cavity. This avoids the influence of the refrigerator's vibration during the cooling process on the frequency of the single-crystal silicon optical cavity. Therefore, regardless of the size of the refrigerator or the degree of vibration, the frequency stability of the single-crystal silicon optical cavity can be measured. Thus, this measurement method is not limited by the cavity length of the single-crystal silicon optical cavity, making it applicable to more application scenarios and highly practical. Attached Figure Description

[0045] To more clearly illustrate the technical solutions in the embodiments of this application or related technologies, the drawings used in the description of the embodiments or prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0046] The structures, proportions, sizes, etc., shown in the accompanying drawings are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed in the specification, and are not intended to limit the implementation conditions of this application. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size should still fall within the scope of the technical content disclosed in this application, provided that they do not affect the effects and purposes that this application can produce.

[0047] Figure 1 A flowchart illustrating a method for measuring the frequency stability of a low-temperature single-crystal silicon optical cavity, provided in this application;

[0048] Figure 2 A comparison of the frequency stability curves of low-temperature single-crystal silicon optical cavities obtained by the measurement method described in this application;

[0049] Figure 3 A flowchart of another method for measuring the frequency stability of a low-temperature single-crystal silicon optical cavity provided in this application;

[0050] Figure 4 A flowchart illustrating another method for measuring the frequency stability of a low-temperature single-crystal silicon optical cavity provided in this application;

[0051] Figure 5 A flowchart illustrating another method for measuring the frequency stability of a low-temperature single-crystal silicon optical cavity provided in this application;

[0052] Figure 6 A flowchart illustrating another method for measuring the frequency stability of a low-temperature single-crystal silicon optical cavity provided in this application;

[0053] Figure 7 A flowchart illustrating another method for measuring the frequency stability of a low-temperature single-crystal silicon optical cavity provided in this application;

[0054] Figure 8 A flowchart illustrating another method for measuring the frequency stability of a low-temperature single-crystal silicon optical cavity provided in this application;

[0055] Figure 9 A flowchart illustrating a method for measuring the frequency stability of a low-temperature single-crystal silicon optical cavity, as provided in this application. Detailed Implementation

[0056] The embodiments of this application will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0057] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0058] As described in the background section, the vibration of the refrigerator causes vibration noise during the measurement of the frequency stability of a single-crystal silicon optical cavity. Specifically, during the cooling process of the single-crystal silicon optical cavity, the refrigerator inevitably shakes the entire experimental setup, causing instability in the cavity length and generating vibration noise induced by the refrigerator vibration, which is reflected in the measured frequency stability. Furthermore, since the vibration noise of the refrigerator is greater than the frequency noise corresponding to the optical performance of the single-crystal silicon optical cavity, it significantly affects the measurement of the frequency stability of the low-temperature single-crystal silicon optical cavity, making it impossible to accurately measure the E-17 level frequency stability inherent in the low-temperature single-crystal silicon optical cavity. Therefore, how to suppress the influence of refrigerator vibration noise on the frequency stability of the single-crystal silicon optical cavity has become a key issue for those skilled in the art.

[0059] For example, how to measure the E-17 level frequency stability inherent in a cryogenic single-crystal silicon optical cavity when E-16 level refrigerator vibration noise exists? Currently, although frequency stability levels of 1E-16 or even 6.5E-17 can be obtained in cryogenic single-crystal silicon optical cavity systems with a cavity length of no more than 6cm, the longer the cavity length, the stronger the required cooling capacity of the refrigerator, and the larger the refrigerator size. This results in stronger vibrations, which have a greater impact on the frequency stability of the single-crystal silicon optical cavity. Therefore, the cavity length of the single-crystal silicon optical cavity is required to be relatively short, no more than 6cm, which is a significant limitation and not conducive to practical applications.

[0060] Based on the above, this application provides a method for measuring the frequency stability of a low-temperature single-crystal silicon optical cavity, such as... Figure 1 As shown, Figure 1 A flowchart of a method for measuring the frequency stability of a low-temperature single-crystal silicon optical cavity is provided in this application. The measurement method includes:

[0061] S1: A single-crystal silicon optical cavity to be tested is provided. Specifically, for example, based on high-purity single-crystal silicon raw materials, a cavity shape (also called an optical cavity) and a cavity mirror shape are fabricated. A high-precision reflective film is deposited on the surface of the cavity mirror, and then the optical cavity and cavity mirror are assembled into a complete optical cavity, thus obtaining a single-crystal silicon optical cavity. After assembling the above-mentioned single-crystal silicon optical cavity, the frequency of a laser can be locked to the cavity length of the single-crystal silicon optical cavity using the traditional and very mature PDH (Pound-Drever-Hall) frequency-locking technology. That is, the laser frequency changes according to the change in the cavity length of the single-crystal silicon optical cavity; in other words, the frequency change of the laser is determined by the change in the cavity length of the single-crystal silicon optical cavity. It should be noted that, for simplicity, the frequency of the single-crystal silicon optical cavity represents the frequency of the laser corresponding to that single-crystal silicon optical cavity, and the frequency stability of the single-crystal silicon optical cavity represents the change in the frequency of the laser corresponding to that single-crystal silicon optical cavity over time.

[0062] S2: The single-crystal silicon optical cavity is cooled using a refrigerator to reduce its temperature to a first preset temperature. This refrigerator can be a GM-type constant-temperature vibration-isolation vacuum refrigerator, meaning it can be used to cool the single-crystal silicon optical cavity from room temperature (20°C) to the first preset temperature. It should be noted that the first preset temperature can be approximately -270°C, meaning the refrigerator can cool the single-crystal silicon optical cavity to approximately -270°C. However, this application does not limit the value of the first preset temperature; it can be any value other than -270°C, depending on the specific circumstances.

[0063] S3: After the temperature of the single-crystal silicon optical cavity is reduced to a first preset temperature, the refrigerator is turned off. During the refrigerator shutdown period, and when the vibration amplitude of the refrigerator drops to a first preset value, the frequency of the single-crystal silicon optical cavity is acquired. It should be noted that although the refrigerator stops cooling after being turned off, the low-temperature state of the single-crystal silicon optical cavity will not change in a short period of time; that is, the temperature of the single-crystal silicon optical cavity will not rise rapidly in a short time. Therefore, during the refrigerator shutdown period, and when the vibration amplitude of the refrigerator drops to the first preset value, the acquired frequency is still the frequency of the single-crystal silicon optical cavity at its low-temperature state, i.e., the frequency of the low-temperature single-crystal silicon optical cavity. It should also be noted that this application does not limit the specific value of the aforementioned first preset value. For example, the first preset value can be zero, but it can also be other values, depending on the specific circumstances.

[0064] S4: Based on the frequency of the single-crystal silicon optical cavity, obtain the frequency stability of the single-crystal silicon optical cavity, that is, based on the frequency of the single-crystal silicon optical cavity obtained in step S3 above, obtain the frequency stability of the single-crystal silicon optical cavity. It should be noted that the frequency stability of the single-crystal silicon optical cavity can characterize the working performance of the single-crystal silicon optical cavity, so obtaining the frequency stability of the low-temperature single-crystal silicon optical cavity can characterize its working performance.

[0065] After the refrigerator is turned off, meaning it stops working, it will no longer vibrate due to its cooling operation. This prevents the experimental platform containing the single-crystal silicon optical cavity from shaking, thus avoiding any impact on the cavity length and consequently, the measurement of its frequency stability. Therefore, when the refrigerator is turned off and its vibration amplitude drops to a first preset value, measuring the frequency stability of the single-crystal silicon optical cavity will not be affected by the refrigerator's vibration. This effectively avoids the influence of the refrigerator's vibration amplitude on the frequency stability measurement of the single-crystal silicon optical cavity, allowing for the acquisition of the frequency stability of the single-crystal silicon optical cavity at low temperatures. It should be noted that the vibration amplitude of the refrigerator is an important determinant of the vibration noise of the refrigerator. Therefore, the measurement method of this application measures the frequency stability of the single-crystal silicon optical cavity when the vibration amplitude of the refrigerator is reduced to a first preset value. That is, this measurement method can measure the frequency stability of the single-crystal silicon optical cavity when the vibration noise of the refrigerator is relatively small, which can effectively reduce the influence of the vibration noise of the refrigerator on the measurement.

[0066] For example Figure 2 As shown, Figure 2 The horizontal axis represents time, and the vertical axis represents the frequency stability of the single-crystal silicon optical cavity. Figure 2 Curve 1 shows the frequency stability curve of the single-crystal silicon optical cavity measured under continuous operation of the refrigerator and with an E-16 level vibration amplitude. Curve 2 shows the inherent frequency stability curve of the single-crystal silicon optical cavity measured by the present method under the same refrigerator vibration amplitude. Based on curves 1 and 2, it can be seen that the measurement method provided in this application can successfully measure the E-17 level frequency stability inherent in the single-crystal silicon optical cavity under the E-16 level vibration amplitude of the refrigerator. Therefore, this measurement method can successfully measure the 6E-17 or even better frequency stability of the single-crystal silicon optical cavity in the liquid helium temperature region under the E-16 level vibration amplitude of the refrigerator, providing experimental means to support the excellent optical performance of the single-crystal silicon optical cavity in the liquid helium temperature region.

[0067] Furthermore, as mentioned above, this measurement method acquires the frequency of the single-crystal silicon optical cavity when the refrigerator is off, thus measuring the frequency stability of the single-crystal silicon optical cavity. This avoids the influence of refrigerator vibration during the cooling process on the frequency of the single-crystal silicon optical cavity. Therefore, regardless of the size of the refrigerator or the degree of its vibration, the frequency stability of the single-crystal silicon optical cavity can be measured. In other words, this method can measure the frequency stability of single-crystal silicon optical cavities with small or large cavity lengths. Therefore, this measurement method is not limited by the cavity length of the single-crystal silicon optical cavity, making it applicable to a wider range of applications and highly practical.

[0068] It should be noted that the frequency of the single-crystal silicon optical cavity is acquired after the temperature is reduced to the first preset temperature, the refrigerator is turned off, and the vibration amplitude of the refrigerator decreases to the first preset value during the refrigerator shutdown period. This is because although the refrigerator has stopped working and no longer generates active vibration due to cooling, there is still a period of vibration relaxation after the refrigerator stops working. Therefore, the frequency of the single-crystal silicon optical cavity is acquired only after the refrigerator is turned off and the vibration amplitude of the refrigerator decreases to the first preset value during the refrigerator shutdown period. This is to minimize the impact of refrigerator vibration on the frequency stability measurement of the single-crystal silicon optical cavity and to obtain the frequency stability of the low-temperature single-crystal silicon optical cavity. It should also be noted that the frequency of the single-crystal silicon optical cavity is only obtained when the vibration amplitude of the refrigerator drops to a first preset value. This is to minimize the impact of refrigerator vibration on the frequency stability measurement of the single-crystal silicon optical cavity. Therefore, the specific value of the first preset value can depend on the tolerance of the refrigerator vibration amplitude when measuring the frequency stability of the single-crystal silicon optical cavity. A larger tolerance allows for a larger first preset value, while a smaller tolerance allows for a smaller first preset value. In other words, when measuring the frequency stability of the single-crystal silicon optical cavity, the accuracy requirement is lower, so the first preset value can be larger; when the accuracy requirement is higher, the first preset value can be smaller. For example, the first preset value mentioned above can be zero.

[0069] In one embodiment of this application, such as Figure 3 As shown, Figure 3 The flowchart provided in this application describes a method for measuring the frequency stability of a low-temperature single-crystal silicon optical cavity. After the temperature of the single-crystal silicon optical cavity drops to a first preset temperature, the refrigerator is turned off. During the refrigerator shutdown period, and when the vibration amplitude of the refrigerator drops to a first preset value, the frequency of the single-crystal silicon optical cavity is obtained, including:

[0070] S31: After the temperature of the single-crystal silicon optical cavity drops to the first preset temperature, the refrigerator is turned off.

[0071] S32: During the period when the refrigerator is off, when the refrigerator changes from the first state to the second state, and during the maintenance of the second state, the frequency of the single-crystal silicon optical cavity is acquired.

[0072] When the refrigeration unit is in the second state, the vibration amplitude of the refrigeration unit is reduced to the first preset value. That is, when the refrigeration unit is in the second state, the vibration amplitude of the refrigeration unit is smaller. Therefore, the vibration amplitude of the refrigeration unit in the first state is greater than the vibration amplitude in the second state.

[0073] After the refrigerator lowers the temperature of the monocrystalline silicon optical cavity to a first preset temperature, it is turned off. The refrigerator then undergoes a relaxation period of approximately 150 seconds, which is the first state described above. Once this vibration relaxation ends, the refrigerator enters a quiet state where its vibration amplitude is at a first preset value. At this point, the refrigerator vibration amplitude can be zero, meaning the refrigerator changes from the first state to the second state, which lasts for approximately 100 seconds. Therefore, after the refrigerator is turned off and changes from the first state to the second state, the refrigerator enters a quiet state with a vibration amplitude at the first preset value, thus avoiding the impact of the refrigerator's vibration amplitude on the frequency stability of the monocrystalline silicon optical cavity. Furthermore, since the low-temperature state of the monocrystalline silicon optical cavity does not change rapidly after the refrigerator is turned off, the impact of the refrigerator's vibration amplitude on the frequency stability of the monocrystalline silicon optical cavity can be avoided, while simultaneously achieving the desired frequency stability, thus enabling the acquisition of the frequency stability of the low-temperature monocrystalline silicon optical cavity.

[0074] In one embodiment of this application, such as Figure 4 As shown, Figure 4 A flowchart of a method for measuring the frequency stability of a low-temperature single-crystal silicon optical cavity provided in this application is included. During the second state maintenance process, obtaining the frequency of the single-crystal silicon optical cavity includes:

[0075] S33: During the first preset time period of the second state maintenance process, the frequency of the single-crystal silicon optical cavity is acquired.

[0076] There is a second preset time between the first preset time and the start time of the second state. The value of the second preset time is greater than 0, and the value of the first preset time can be 40s to 60s, including the endpoint value.

[0077] After the refrigerator is turned off, its vibration amplitude should gradually decrease, or rather, it should go from present to absent. Therefore, after the refrigerator changes from the first state to the second state, the vibration amplitude of the refrigerator is at the first preset value throughout the second state. Based on this, the frequency of the single-crystal silicon optical cavity is obtained within the first preset time period during the maintenance of the second state, that is, the frequency of the single-crystal silicon optical cavity is obtained during the time period when the vibration amplitude of the refrigerator is at the first preset value. This can help to avoid the influence of the refrigerator's vibration amplitude on the frequency stability of the single-crystal silicon optical cavity.

[0078] It should be noted that the value of the first preset time can be in the range of 40s to 60s, including the endpoint value. Preferably, the value of the first preset time can be 50s. However, this application does not limit the range or specific value of the first preset time, but depends on the specific circumstances.

[0079] In one embodiment of this application, such as Figure 5 As shown, Figure 5 The flowchart provided in this application describes a method for measuring the frequency stability of a low-temperature single-crystal silicon optical cavity. After the temperature of the single-crystal silicon optical cavity drops to a first preset temperature, the refrigerator is turned off. During the refrigerator shutdown period, and when the vibration amplitude of the refrigerator drops to a first preset value, the method for obtaining the frequency of the single-crystal silicon optical cavity further includes:

[0080] S34: During the second state maintenance process, the temperature of the single-crystal silicon optical cavity is obtained.

[0081] S35: If the temperature of the monocrystalline silicon optical cavity is higher than the second preset temperature, stop acquiring the frequency of the monocrystalline silicon optical cavity and start the cooler to cool the monocrystalline silicon optical cavity back down to the first preset temperature. For example, if the temperature of the monocrystalline silicon optical cavity rises significantly, i.e., the temperature of the monocrystalline silicon optical cavity is higher than the second preset temperature, restart the cooler and wait for the cooler to run for 2-3 hours to lower the temperature of the monocrystalline silicon optical cavity back down to the first preset temperature (around -270℃).

[0082] S36: After the temperature of the single-crystal silicon optical cavity is reduced back to the first preset temperature, the refrigerator is turned off, and during the period when the refrigerator is turned off and the vibration amplitude of the refrigerator is reduced to the first preset value, the frequency of the single-crystal silicon optical cavity is obtained.

[0083] Since the refrigerator stops cooling the monocrystalline silicon optical cavity after it is turned off, the cavity's temperature will gradually rise. Therefore, during the second state maintenance process—more precisely, during the frequency acquisition of the monocrystalline silicon optical cavity—frequent or periodic temperature measurements of the cavity are necessary. If the cavity temperature rises significantly and no longer meets the temperature requirements for a low-temperature monocrystalline silicon optical cavity, frequency acquisition is stopped, the refrigerator is restarted, and the cavity is cooled again until it returns to the first preset temperature. In other words, this measurement method can briefly remove the refrigerator's vibration amplitude, repeatedly acquire the cavity frequency, and calculate the frequency stability of each acquisition. The average frequency stability is obtained by averaging these multiple acquisitions. This method can acquire the frequency stability of the monocrystalline silicon optical cavity based on a large amount of data, resulting in highly accurate frequency stability measurements.

[0084] It should be noted that when this measurement method obtains the frequency stability of a single-crystal silicon optical cavity based on the frequency of the single-crystal silicon optical cavity acquired repeatedly, the frequency stability of the single-crystal silicon optical cavity is calculated once for each acquisition of the single-crystal silicon optical cavity frequency, and then the final average frequency stability is obtained based on the frequency stability of the single-crystal silicon optical cavity acquired multiple times.

[0085] It should also be noted that after the temperature of the single-crystal silicon optical cavity is lowered back to the first preset temperature, the refrigerator should not be shut down immediately to acquire the frequency of the single-crystal silicon optical cavity. Instead, the refrigerator should be run for a period of time after the temperature of the single-crystal silicon optical cavity has been lowered back to the first preset temperature to stabilize the low temperature state of the single-crystal silicon optical cavity. That is, the refrigerator should only be shut down and subsequent steps should be carried out after the temperature of the single-crystal silicon optical cavity has been lowered back to the first preset temperature and the single-crystal silicon optical cavity has been stably in a low temperature state.

[0086] In one embodiment of this application, such as Figure 6 As shown, Figure 6 The flowchart provided in this application describes a method for measuring the frequency stability of a low-temperature single-crystal silicon optical cavity. The method involves cooling the single-crystal silicon optical cavity using a refrigerator to lower its temperature to a first preset temperature, including:

[0087] S21: Place the single-crystal silicon optical cavity into the sample chamber of the refrigerator.

[0088] S22: Use the first vacuum pumping device to perform the first vacuum pumping on the sample chamber of the refrigerator, and pump the sample chamber of the refrigerator to the first vacuum level.

[0089] S23: The sample chamber of the refrigerator is evacuated a second time using a second vacuum pumping device, bringing it to a second vacuum level. The second vacuum level represents a higher degree of vacuum than the first vacuum level.

[0090] S24: After the sample chamber of the refrigerator is evacuated to the second vacuum level, the refrigerator is used to cool the single-crystal silicon optical cavity, reducing the temperature of the single-crystal silicon optical cavity to the first preset temperature.

[0091] The first vacuum pumping device can be a cascaded molecular pump, and the second vacuum pumping device can be an ion pump. The first vacuum level can be 1E-6 Torr, and the second vacuum level can be 3E-7 Torr. Specifically, after placing the single-crystal silicon optical cavity in the sample chamber of the refrigerator, before the refrigerator starts cooling, at room temperature, the cascaded molecular pump group is first used to pump the vacuum level of the refrigerator sample chamber to 1E-6 Torr. Then, an ion pump with a pumping speed of 45 L / s is used to pump the vacuum level of the refrigerator to 3E-7 Torr. Subsequently, the cold head of the refrigerator is turned on to start cooling. After running continuously for 5 days, the single-crystal silicon optical cavity can be cooled from room temperature of 20 degrees Celsius to the first preset value (approximately -270 degrees Celsius), completing the cooling of the single-crystal silicon optical cavity.

[0092] In one embodiment of this application, such as Figure 7 As shown, Figure 7 This application provides a flowchart of a method for measuring the frequency stability of a low-temperature single-crystal silicon optical cavity, which includes a single-crystal silicon optical cavity comprising:

[0093] S11: Provides a single-crystal silicon optical cavity with a cavity length of the first cavity length.

[0094] S12: Provides a first reference cavity with a cavity length of the second cavity length.

[0095] S13: A second reference cavity with a length of the third cavity length is provided. The temperature difference between the first and second reference cavities is no greater than a second preset value; that is, the temperature difference between the first and second reference cavities can be small, thus allowing their temperatures to be similar, or even approximately the same. Furthermore, the temperature range of the first and second reference cavities is 15℃ to 30℃, including the endpoints. It should be noted that the temperature of the first and second reference cavities can be room temperature (20℃), but this application does not limit this; it depends on the specific circumstances. It should also be noted that the temperatures of the first and second reference cavities can be significantly different, but to reduce variable factors in the frequency stability acquisition process of the single-crystal silicon optical cavity, the first and second reference cavities are preferably made of materials with the same or similar properties and operate at the same or similar temperatures.

[0096] As described above, this measurement method employs the triangular cap precision frequency measurement method to obtain the frequency stability of a single-crystal silicon optical cavity. Specifically, the triangular cap precision frequency measurement method requires the construction of a triangular cap measurement system. This means that, based on the aforementioned single-crystal silicon optical cavity, two reference cavities are needed, and the frequencies of the lasers corresponding to these two reference cavities are locked to the cavity lengths of their respective optical cavities. These are the first and second reference cavities, respectively, to construct the triangular cap measurement system required for the triangular cap precision frequency measurement method, providing a measurement basis for obtaining the frequency stability of the single-crystal silicon optical cavity.

[0097] In one embodiment of this application, such as Figure 8 As shown, Figure 8 The flowchart provided in this application describes a method for measuring the frequency stability of a low-temperature single-crystal silicon optical cavity. After the temperature of the single-crystal silicon optical cavity drops to a first preset temperature, the refrigerator is turned off. During the refrigerator shutdown period, and when the vibration amplitude of the refrigerator drops to a first preset value, the frequency of the single-crystal silicon optical cavity is obtained, including:

[0098] S37: During the period when the refrigerator is off and the vibration amplitude of the refrigerator drops to a first preset value, the frequency of the single-crystal silicon optical cavity is acquired.

[0099] S38: While acquiring the frequency of the single-crystal silicon optical cavity, the frequencies of the first reference cavity and the second reference cavity are also acquired.

[0100] In one embodiment of this application, the following continues... Figure 7 As shown, the frequency stability of a single-crystal silicon optical cavity is obtained based on its frequency, including:

[0101] S41: The frequency stability of the single-crystal silicon optical cavity is obtained based on the frequency difference between any two of the three cavities: the single-crystal silicon optical cavity, the first reference cavity, and the second reference cavity.

[0102] The frequency stability of the single-crystal silicon optical cavity is obtained by considering the frequency differences between any two of the three cavities: the single-crystal silicon optical cavity, the first reference cavity, and the second reference cavity.

[0103] The frequency stability of the single-crystal silicon optical cavity is obtained based on the first frequency difference, the second frequency difference, and the third frequency difference. The first frequency difference is the frequency difference between the single-crystal silicon optical cavity and the frequency of the first reference cavity; the second frequency difference is the frequency difference between the single-crystal silicon optical cavity and the frequency of the second reference cavity; and the third frequency difference is the frequency difference between the first reference cavity and the second reference cavity.

[0104] As described above, after setting up the measurement system required for the triangular cap measurement, this measurement method obtains the frequency difference between the frequency of the single-crystal silicon optical cavity and the frequency of the first reference cavity, the frequency difference between the frequency of the single-crystal silicon optical cavity and the frequency of the second reference cavity, and the frequency difference between the frequencies of the first and second reference cavities. Then, based on these frequency difference settings, the frequency difference data is analyzed using the triangular cap precision frequency measurement method to obtain the frequency stability of the single-crystal silicon optical cavity.

[0105] In one embodiment of this application, both the first and second reference cavities are made of ULE glass. Since ULE glass (Ultra-Low Expansion Glass) is a material with an extremely small, even zero, coefficient of thermal expansion, its cavity length will not change due to the thermal expansion of the first and second reference cavities. This ensures the stability of the cavity lengths of both cavities and does not affect the accuracy of measuring the frequency stability of the single-crystal silicon optical cavity, thus allowing for accurate acquisition of the frequency stability of the single-crystal silicon optical cavity.

[0106] In one embodiment of this application, the lengths of the first cavity, the second cavity, and the third cavity can be equal, or they can be unequal, or the first cavity length and the second cavity length can be unequal, while the second cavity length and the third cavity length are equal. In other words, when measuring the frequency stability of a single-crystal silicon optical cavity using this measurement method, the relative cavity lengths between the single-crystal silicon optical cavity, the first reference cavity, and the second reference cavity are unrestricted and can be flexibly set. Therefore, this measurement method is applicable to more application scenarios and has strong practicality.

[0107] Optionally, the length of the second cavity can be 30cm, and the length of the third cavity can also be 30cm, but this application does not limit this and it depends on the specific circumstances.

[0108] To provide a clearer understanding of the method for measuring the frequency stability of a single-crystal silicon optical cavity provided in this application, a flowchart is provided below to describe the measurement method in detail.

[0109] like Figure 9As shown, the refrigerator is started to cool the monocrystalline silicon optical cavity to a first preset temperature. The refrigerator is then turned off, and it sequentially enters a relaxation state (first state) and a quiet state (second state). While the refrigerator is in the quiet state, frequency stability is measured using the triangular cap precision frequency measurement method. Simultaneously, the temperature of the monocrystalline silicon optical cavity is measured. When the temperature of the monocrystalline silicon optical cavity rises significantly, the measurement is stopped, and the refrigerator is restarted to cool the cavity. After the temperature of the monocrystalline silicon optical cavity is reduced to the first preset temperature, the refrigerator is turned off again. Then, while the refrigerator is in the quiet state, the triangular cap precision frequency measurement method is used again for measurement and analysis to measure frequency stability. The above steps are repeated until the obtained frequency data and frequency stability data of the monocrystalline silicon optical cavity meet the requirements for subsequent calculations.

[0110] The various embodiments in this specification are described in a progressive, parallel, or combined manner. Each embodiment focuses on its differences from other embodiments, and similar or identical parts between embodiments can be referred to interchangeably. For the apparatuses disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple, and relevant parts can be referred to the method section.

[0111] It should be noted that, in the description of this application, the terms "upper," "lower," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. When a component is considered to be "connected" to another component, it can be directly connected to the other component or there may be a component centrally located at the same time.

[0112] It should also be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or apparatus comprising a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or apparatus that includes the aforementioned element.

[0113] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for measuring the frequency stability of a low-temperature single-crystal silicon optical cavity, characterized in that, include: Provide a single-crystal silicon optical cavity to be tested; The temperature of the single-crystal silicon optical cavity is reduced to a first preset temperature by using a refrigerator. After the temperature of the single-crystal silicon optical cavity drops to the first preset temperature, the refrigerator is turned off. During the period when the refrigerator is turned off, and when the vibration amplitude of the refrigerator drops to the first preset value, the frequency of the single-crystal silicon optical cavity is obtained. The frequency stability of the single-crystal silicon optical cavity is obtained based on its frequency.

2. The method for measuring the frequency stability of a low-temperature single-crystal silicon optical cavity according to claim 1, characterized in that, After the temperature of the single-crystal silicon optical cavity drops to the first preset temperature, the refrigerator is turned off. During the period when the refrigerator is off, and when the vibration amplitude of the refrigerator drops to the first preset value, the frequency of the single-crystal silicon optical cavity is obtained, including: After the temperature of the single-crystal silicon optical cavity drops to the first preset temperature, the refrigerator is turned off. During the period when the refrigerator is off, when the refrigerator changes from a first state to a second state, and during the maintenance of the second state, the frequency of the single-crystal silicon optical cavity is acquired; When the refrigeration unit is in the second state, the vibration amplitude of the refrigeration unit is reduced to the first preset value, and the vibration amplitude of the refrigeration unit in the first state is greater than the vibration amplitude in the second state.

3. The method for measuring the frequency stability of a low-temperature single-crystal silicon optical cavity according to claim 2, characterized in that, During the maintenance of the second state, the frequency of the single-crystal silicon optical cavity is obtained including: During the first preset time period of the second state maintenance process, the frequency of the single-crystal silicon optical cavity is obtained; There is a second preset time between the first preset time and the start time of the second state. The value of the second preset time is greater than 0, and the value of the first preset time is in the range of 40s to 60s, including the endpoint value.

4. The method for measuring the frequency stability of a low-temperature single-crystal silicon optical cavity according to claim 2, characterized in that, After the temperature of the single-crystal silicon optical cavity drops to the first preset temperature, the refrigerator is turned off. During the period when the refrigerator is off, and when the vibration amplitude of the refrigerator drops to the first preset value, obtaining the frequency of the single-crystal silicon optical cavity further includes: During the maintenance of the second state, the temperature of the single-crystal silicon optical cavity is acquired; If the temperature of the single-crystal silicon optical cavity is higher than the second preset temperature, the acquisition of the frequency of the single-crystal silicon optical cavity is stopped, and the refrigerator is started to cool down the single-crystal silicon optical cavity to the first preset temperature. After the temperature of the single-crystal silicon optical cavity is reduced back to the first preset temperature, the refrigerator is turned off, and during the period when the refrigerator is turned off, and when the vibration amplitude of the refrigerator is reduced to the first preset value, the frequency of the single-crystal silicon optical cavity is obtained.

5. The method for measuring the frequency stability of a low-temperature single-crystal silicon optical cavity according to claim 1, characterized in that, Cooling the single-crystal silicon optical cavity using a refrigerator to reduce its temperature to a first preset temperature includes: The single-crystal silicon optical cavity is placed in the sample chamber of the refrigerator; The sample chamber of the refrigerator is evacuated for the first time using the first vacuum pumping device to bring the sample chamber of the refrigerator to a first vacuum level. The sample chamber of the refrigerator is evacuated a second time using a second vacuum device to bring it to a second vacuum level; wherein the second vacuum level represents a higher degree of vacuum than the first vacuum level. After the sample chamber of the refrigerator is evacuated to the second vacuum level, the refrigerator is used to cool the single-crystal silicon optical cavity, reducing the temperature of the single-crystal silicon optical cavity to the first preset temperature.

6. The method for measuring the frequency stability of a low-temperature single-crystal silicon optical cavity according to claim 1, characterized in that, A single-crystal silicon optical cavity is provided, comprising: The single-crystal silicon optical cavity is provided with a cavity length of a first cavity length; Provide a first reference cavity with a cavity length of the second cavity length; Provide a second reference cavity with a cavity length of the third cavity length; Wherein, the temperature difference between the first reference cavity and the second reference cavity is not greater than a second preset value, and the temperature range of the first reference cavity and the second reference cavity is 15℃~30℃, including the endpoint value.

7. The method for measuring the frequency stability of a low-temperature single-crystal silicon optical cavity according to claim 6, characterized in that, After the temperature of the single-crystal silicon optical cavity drops to the first preset temperature, the refrigerator is turned off. During the period when the refrigerator is off, and when the vibration amplitude of the refrigerator drops to the first preset value, the frequency of the single-crystal silicon optical cavity is obtained, including: After the temperature of the single-crystal silicon optical cavity drops to the first preset temperature, the refrigerator is turned off. During the period when the refrigerator is turned off, and when the vibration amplitude of the refrigerator drops to the first preset value, the frequency of the single-crystal silicon optical cavity is obtained. Furthermore, while acquiring the frequency of the single-crystal silicon optical cavity, the frequencies of the first reference cavity and the second reference cavity are also acquired.

8. The method for measuring the frequency stability of a low-temperature single-crystal silicon optical cavity according to claim 6, characterized in that, Based on the frequency of the single-crystal silicon optical cavity, the frequency stability of the single-crystal silicon optical cavity is obtained by: The frequency stability of the single-crystal silicon optical cavity is obtained based on the frequency differences between any two of the single-crystal silicon optical cavity, the first reference cavity, and the second reference cavity. The frequency stability of the single-crystal silicon optical cavity is obtained based on the frequency differences between any two of the three cavities: the single-crystal silicon optical cavity, the first reference cavity, and the second reference cavity. The frequency stability of the single-crystal silicon optical cavity is obtained based on the first frequency difference, the second frequency difference, and the third frequency difference. The first frequency difference is the frequency difference between the frequency of the single-crystal silicon optical cavity and the frequency of the first reference cavity, the second frequency difference is the frequency difference between the frequency of the single-crystal silicon optical cavity and the frequency of the second reference cavity, and the third frequency difference is the frequency difference between the frequency of the first reference cavity and the frequency of the second reference cavity.

9. The method for measuring the frequency stability of a low-temperature single-crystal silicon optical cavity according to claim 6, characterized in that, The first reference cavity is made of ULE glass, and the second reference cavity is made of ULE glass.

10. The method for measuring the frequency stability of a low-temperature single-crystal silicon optical cavity according to claim 6, characterized in that, The lengths of the first cavity, the second cavity, and the third cavity are equal; or The lengths of the first cavity, the second cavity, and the third cavity are not equal; or The lengths of the first cavity and the second cavity are not equal, while the lengths of the second cavity and the third cavity are equal.

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